All of the above. Moving large bodies of men over difficult terrain disrupted their formations and made them more vulnerable to enemy fire and eventual panic. The ground in front of Marye's Heights was broken by several such terrain features and ended in front of a sunken road and stone wall that formed a formidable breastwork for the Confederate defenders. The Union attacks disintegrated as they made the approach.

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Answer:

All of the above. Moving large bodies of men over difficult terrain disrupted their formations and made them more vulnerable to enemy fire and eventual panic. The ground in front of Marye's Heights was broken by several such terrain features and ended in front of a sunken road and stone wall that formed a formidable breastwork for the Confederate defenders. The Union attacks disintegrated as they made the approach.